There are a number of known techniques for physically characterizing irregularly shaped objects. These techniques, which are used primarily for sorting operations, are based upon analysis of light reflected from the objects being characterized. For example, in U.S. Pat. No. 3,357,557, a technique is disclosed for using reflected light as a means of determining the flatness of semi-conductor chips. In U.S. Pat. No. 4,057,146, beans, grain and similar produce are sorted by size and color analysis as a result of light being reflected from the produce. Similarly, various types of ores have been sorted as a function of light reflectance. In this regard, mention is made of U.S. Pat. Nos. 3,097,744; 3,901,388; and U.S. Pat. No. 3,977,526. In addition to the foregoing, mention also is made of ore sorters which use lasers as the light source, such as disclosed in U.S. Pat. No. 3,545,610 and U.S. Pat. No. 4,122,952, and ore sorters which use infrared light as the light source, such as disclosed in U.S. Pat. No. 4,236,640.
One of the disadvantages of devices for optical characterization of objects which are based upon color or reflectance as a characterizing criteria is that use of such devices is limited to applications where there are significant color or light reflectance differences between different classes of the objects being characterized. In the minerals processing field, for example, commercial use of such optical devices for sorting ores generally has been limited to sorting sheelite from gangue and magnesite from gangue since the minerals being sorted possess special fluorescent and reflectance properties making the sort possible. Many minerals and, indeed, other objects requiring sorting do not have the requisite optical properties rendering them susceptible to sorting based on their surface properties. Thus, there remains a need for means to characterize and sort or otherwise treat randomly oriented irregularly shaped objects from a stream of objects.